Composition of matter



Patented Jan. 22, 1946 UNITED STATES PATENT OFFICE COMPOSITION OF MATTER Edward L. Carr, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Original application September'27,

1941, Serial No. 412,685. Divided and this application October 8, 1943, Serial No. 505,569

Claims.

This invention relates to a new class 01! chemical compounds which are valuable accelerators for the vulcanization of rubber or rubber-like substances. This specification is a division of my application serial No. 412,685, filed September 27, 1941, now Patent No. 2,339,552, which was, in turn, a continuation in part of my application Serial No. 259,712, filed March 3, 1939-, now Patent No. 2,271,834..

It is a primary object of, the present invention to provide a new class of accelerators for the vulcanization of natural or synthetic rubber.

Another object is to provide a class of improved rubber vulcanization accelerators of the delayed action, non-scorching type.

The above and further objects will be manifest in the description of the invention which follows.

It has been found that members of a new class' of chemical compounds are very eifectiv'e'in accelerating, the. vulcanization of natural, or syn-.

thetic rubber. The new compounds may be c.on-' veniently prepared by oxidizing a mixture of an aromatic Z-mercaptothiazole and an ammonia derivative of the formula R1NH2, wherein R1 example of an arylenethiazylthioamino-substituted alkyl radical is =beta-(2-benzothiazylthioamino)-ethyl, illustrated in certain of the 01- represents an alkyl radical or an amino.-substi-.

tuted alkyl radical. reaction may be eiiected by treating a mixture of the mercaptothiazole and an excess ofthe ammonia derivative in an alkaline aqueous medium with one of the following oxidizing agents: chlorine, bromine, iodine, hypochlorous acid, hypobromous acid, hypoiodous acid, and alkali metal and alkaline earth metal salts of said acids. The oxidation reaction is thought to. comprise the: direct action of a hypohalous acid, or an alkali metal or an alkaline earth metal salt thereof, on a mixture of the mercaptothiazole and one equivalent of the ammonia derivative. The desired substances produced by this oxidation re- The preparative oxidation lowing examples.

The following specific examples are given in further illustration of the invention.

Example 1 An aqueous solution was prepared containing 10 grams of mercaptobenzothiazole, 4.8 grams of sodium hydroxide and 21 grams of commercial mixed monoamylamines in a volume of 250 cc. To this solution there were added with stirring 200 cc. of a solution containing 15.3 grams of iodine and 16 grams of potassium iodide. The product was obtained as an oil, which, on being washed and dried, set to a semi-crystalline condition. The yield was practically quantitative. The product is believed to be a mixture of N- amyl-Z-benzothiazyl sulfenamides of the structure action are organic compounds containing nitrogen and sulfur.

This new class of accelerators is believed to possess the following type formula:

i Ar \O-S-N-R The above reaction product was tested as an accelerator by comparing it with the standard accelerator, mercaptobenzotlriiazole, as a control, in the following rubber formula:

The two rubber compositions, so formulated, were vulcanized at 280 F. for 20 minutes. Test pieces of the vulcanized stocks were subjected to physical testing, the results of which are as follows:

Modulus of elasticity Tensile in lbs/in. strength The foregoing data clearly show that the mixed N-amyl-2-benzothiazyl sulfenamides constitute a very effective rubber accelerator, imparting high modulus and tensile characteristics to-a rubber composition in a very short curing time.

Example 2 A solution was prepared containing grams of mercaptobenzothiazole, 2.4 grams of sodium hydroxide and excess concentrated ammonia in a volume of 100 cc. To this solution there was added with stirring a 10 per cent solution of sodium hypochlorite until the reaction mixture was depleted of mercaptobenzothiazole, as shown by a lack of precipitation of the same on acidifying a filtered sample of the reaction mixture. The product was obtained in high yield as a White precipitate, which, after being washed with water and dried, melted at 125 C. The compound is believed to be 2-benzothiazyl sulfenamide of the structure C-S-NH:

The above reaction product was tested as an accelerator by comparing it with mercaptobenzothiazole in the rubber formula set out in Example the curing time being minutes at 280 F. The physical testing results are as follows:

Modulus of Tensile elasticity strength Accelerator in lbsJinJ lbs./

at elongain. at tion of 600% break Mercaptobenzothiazole 700 2, 425 z-benzothiazyl sulfenamide l, 450 3, 700

The above data show that 2-benzothiazyl sulfenamide is an efiicient rubber accelerator, imparting high modulus and tensile characteristics to a rubber composition in a short cure.

Example 3 .then dried in a vacuum. The oil partially crystallized to a thick paste. The yield was 13.6 grams or 95 per cent of the theoretical. The product is'believed to be a mixture of N-butyl-Z-benzothiazyl sulfenamides of the structure The above reaction product was tested as an accelerator by comparing it with mercaptobenzothiazole in the rubber formula set out in Exampie 1, the curing time being 20 minutes at 280 F. The physical testing results follow:

Modulus of elasticity 52 2% Accelerator in lbs/in. in lbs [in at elouga at break tion of 600% Mercaptobenzothiazole 700 2, 425 N-butyl-Z-benzothlazyl sulfenamides 2, 150 3, 450

Thesetesting data demonstrate the high accelerating characteristics of the mixed N-butyl- 2-benzothiazyl sulfenamides.

Example 4 When the chemical preparation procedure described in the foregoing examples was applied to mixtures of mercaptobenzothiazole separately, with methylamine, ethylamine and n-propylamine, the following sulfenamides were obtained:

Bulfenamide Physical condition N-methyl-Z-benmthiazyl Amber liquid. N-ethyl-Z-benzothiazyl White solid, M. P. 55-57 C. N-n-propyl-2-benzothiazyl White solid, M. P. 32-33" C.

v to determine whether or not they possessed any tendency to pre-vulcanize or set-up during processing steps prior to the usual vulcanizing step, and the following physical testing data were obtained:

Other'samples of the aforesaid rubber compositions were heated for 20 minutes at 280 F. to determine the relative accelerating properties of the respective accelerators, and the following physical testing data were obtained:

Modulus Tensile ig ig streiggth a Accelerator Leia/11:15

ggg break Mercaptobenzothiazole 800 2, 825 Dibenzothiazyl disulfide 600 2, 550 N-methyl-Z-benzotbiazyl sulfenamide 2, 050 3, 725 N-ethyl-Z-benzothiazyi sulfenamide 2. 625 3. 825 N-n-propyl-2-benzothiazyl sulienamide 2, 475 3, 625

aaeaooo The two sets of testing data given above show that the three new sulfenamide derivativesare excellent delayed-action accelerators, since rubber compositions including them did not vulcanize at the relatively low temperature of 240 F., in contrast with the composition including the standard accelerator, mercaptoben'zothiazole; and the three new accelerators imparted. very high physical-properties to: the rubber composition aftera short cure at 230 F., in comparison with mercaptobenzothiazole and the standard delayed-action accelerator, dibenzothiazyl disulfide.

Example The chemical procedure of Example 3 was applied to n-butylamine and mercaptobenzothiazole to produce N-n-butyl-Z-benzothiazyl sulfenamide, a white solid melting at 35-37' C. This substance was tested in the rubber formula set out in Example 1, in comparison with the control accelerators, mercaptobenzothiazole and dibenzothiazyl disulfide. When samples of the three test compositions were heated for 30 minutes at 240 F., the composition containing the sulfenamide derivative and the composition containing dibenzothiazyl disulfide were not set-up or vulcanized, but the composition containing mercaptobenzothiazole was vulcanized, to the extent shown in Example 4. Other samples of the three test compositions were heated for 40 minutes at 280 F., and the following physical data were obtained.

The above data clearly indicate that the n-butyl derivative is a highly effective delayed action accelerator.

" Example 6 To 100 cc. of a stirred solution containing 10 grams of mercaptobenzothiazole, 2.4 grams of sodium hydroxide and 30 grams of ethylene diamine there was slowly added, with stirring, a 5 per cent solution of sodium hypochlorite. The reaction product precipitated as white crystals melting at 115 C., and is believed to be a mixture of N-betaamino-ethyl-2-benzothiazyl sulfenamide of the and N-beta-(Z-benzothiazylthioamino) -ethyl-2- benzothiazyl sulfenamide of the formula o-s-n-cmom-rr-s-c The above reaction product, as well as similar reaction products of mercaptoarylenethiazoles and propylene diamine, pentamethylene diamine, hexamethylene diamine, or diethylene triamine, are eflective rubber vulcanization accelerators,

comparable with the foregoing reaction products derived from unsubstituted alkyl primary amines.

Example 7 A solution. was prepared containing. 16.! grams of mercaptobenzothiazole, 4.0 grams of sodium hydroxide and 28 grams of ethylene diamine. To this solution there were slowly added, with stirring, 150 cc. of 5.25 per cent sodium hypochlorite solution. A white, finelydivided precipitate was produced, and this precipitate was then recrystallized from alcohol. Six grams of the purified product was thereby obtained, melting at 125- 126 C. This purified product is believed to be substantially N-beta-(2-benzothiazylthioamino) ethyl-2-benzothiazyl sulfenamide.

The purified reaction product was tested as an accelerator, according to the procedure of Example 1, the test rubber compositions being heated at 280 C. for 20 minutes. The following data were obtained:

The above data show that the reaction product of mercaptobenzothiazole and ethylenediamine is a superior rubber accelerator.

Members of the preferred class of accelerators may be prepared in any suitable manner, the methods described above being given for illustration only. The accelerators are equally effective in rubber tread compounds, latex compounds or other conventional vulcanizable compounds of rubber or synthetic rubber. The various vulcanizable synthetic rubbers are herein considered equivalent to rubber, examplesbeing the Buna types (polymers essentially derived from butadiene), such as Buna N (copolymer of butadiene and acrylonitrile) and Buna S (copolymer of butadiene and styrene). Although sulfur has hereinabove been mentioned as the vulcanizing agent preferred in practicing the invention, other conventional vulcanizing agents susceptible to acceleration are contemplated.

The preferred compounds are seen to be very rapid accelerators at conventional vulcanizing temperatures, but are of the delayed action type, in that vulcanizable compositions including them do not set-up or pre-vulcanize under conventional rubber processing conditions. The vulcanized products have been found to be highly efiicient, having low hysteresis characteristics, and to be unusually resistant to deterioration on flexing or aging.

wherein Ar is an orthoarylene radical and R is 3. An N-butyl-Z-benzothiazyl sulfenamide havan alkyl radical. 7 7 ing the formula 2. An N-amyl-2-benz0thiazyl sulfenamide hav- N ing the formula, H v N\ H r v 5 c-s-15-0di.

" C- s -l I-clHn I I V S s 4. N-n-amyl-Z-benzothiazyl sulfenamide.

5. N-n-butyl-2-benzothiazy1sulfenamide.

EDWARD L. CARR. 

